Lithography techniques are widely applied to the manufacture of microstructures of a variety of electronic devices such as semiconductor devices and liquid crystal devices. As electronic devices get miniaturized, the need for micropatterning resists increasingly becomes more important in lithography processes. In the fabrication of micropatterns of 90 nm or finer, developing an exposure device and a resist corresponding to it becomes the key issue. Generally, using short-wavelength light sources such as F2 excimer laser, extreme ultraviolet (EUV), electron beam, X-rays, and soft X-rays and increasing the numerical aperture (NA) of lenses are the focuses in the development of exposure devices. However, expensive new exposure devices are required for the shift to short-wavelength light sources. Meanwhile, the increase in the NA causes a trade-off relation between the resolution and the focal-depth range, so that an increase in resolution is accompanied by a reduction in the focal-depth range.
Liquid immersion lithography is a lithographic process capable of solving this problem. In liquid immersion lithography, at least one liquid, such as pure water, a fluorine-based inert liquid, or the like is placed on a resist layer upon a substrate to a predetermined thickness so that a liquid immersion medium (immersion solution, liquid having a refractive index, etc.) can be interposed between a lens and a resist layer during the exposure process. As a result, an inert gas such as air and nitrogen that has been filling the light path during an exposure process is replaced with a liquid immersion medium having a refractive index greater than that of the inert gas, for example, pure water. Through such replacement, a higher resolution is obtained while preventing deterioration in the focal-depth range despite using a light source of the same wavelength for exposure, as in the case of a shorter-wavelength light source or a higher NA lens. Thus, liquid immersion lithography provides an inexpensive technique capable of forming a resist pattern having both a high resolution and a wide focal-depth range with a lens already mounted on a pre-existing device, and hence, much attention has been paid to liquid immersion lithography.
However, because a resist film directly contacts a liquid immersion medium during an exposure process of liquid immersion lithography, invasion by the liquid may occur. In addition, the resist material may leach out to the surroundings due to the liquid immersion medium.